Neocarzinostatin (NCS), an antibiotic protein isolated from Streptomyces carzinostaticus, is active in experimental tumors in mice. It is in Phase I and II studies in this country including the Sidney Farber Cancer Institute (SFCI). We have been investigating several aspects of NCS and the significant results were: a) establishment of the amino acid sequence and secondary structure of the protein, b) preparation of biologically active analogs, c) development of a radioimmunoassay procedure, d) organ and tissue distribution of NCS in normal and tumor bearing animals, and most significantly, e) demonstration of a possible cell surface mode of action for NCS to induce cytotoxicity in leukemic cells (CCRF-CEM) in vitro. With the knowledge gained thus far, we propoe to continue investigations on NCS which include the folloing: a) chemical and enzymatic modification of NCS to isolate an active "core", b) covalent coupling of NCS to albumin, gamma-globulin, F(ab)2 fragments and soluble synthetic polymers in an effort to increase stability, transport, and half-life of NCS in the body, and c) kinetics of binding of NCS to leukemic cells and the effects of NCS binding on the biochemical changes in the cell. We also propose to identify and to isolate a resistant cell line among the existing established lines: comparative studies on binding of NCS in sensitive and resistant cells may result in understanding the mechanism of natural as well as induced resistance. Since NCS is suggested to have an entirely different mechanism of action, compared to other anticancer agents, the investigations projected in this application may eventually lead to better clinical usage of NCS through tumor-specific binding and target-oriented transport.